The present invention relates to a method and apparatus for planing an article of wood, such as may be used for planing logs or cut lumber in a lumber mill.
Wood that is first obtained in the form of logs generally must be processed to provide finished lumber for use in construction. One step that is often necessary is to plane the surface of the log or the cut lumber. This may be a secondary, finishing process, but is often an aspect of the primary process in which cutting chips are removed from raw logs.
Planing apparatus typically employ drum-style surfacing or chipping heads, herein xe2x80x9ccutting heads,xe2x80x9d which include a rotating cylinder on which is mounted a plurality of knives for cutting the surface of the wood, which may be lumber or logs. The wood is fed while supported on a horizontal support surface along a generally horizontal path that results in the grazing of the top surface of the wood by the knives. Wood chips or finer particulates are thereby removed from the top surface of the wood to a predetermined depth.
Each knife is typically clamped in the apparatus between an outer clamping member and an inner clamping member or counterknife, wherein the knife and counterknife together form a surface against which the log is forced in order to remove the wood chips. The knife has a cutting edge that is parallel to the axis of rotation of the cutting head.
In a specific process known as xe2x80x9cprofiling,xe2x80x9d curved or wany edges of raw logs are removed, and it is preferable that this process also leave behind flat surfaces of smooth finish. The profiling head cuts a corner that extends along the length of the log and that defines an outer side of one board and at least part of the upper or lower face of an adjacent board. To cut the corner, the profiling head rotates about an axis and has cutting surfaces oriented at right angles with respect to each other.
The profiling head may include a knife for planing the aforementioned upper or lower face in the example given above, the cutting head of the knife cutting a plane that is parallel to the axis of rotation of the cutting head (xe2x80x9cfacing cutxe2x80x9d) for cutting the aforementioned face, and a saw or knife for cutting the aforementioned outer side (xe2x80x9cslicing cutxe2x80x9d), which defines a plane that is perpendicular to the axis of rotation. The requirements for the knife or knives employed for the facing cut in the profiling head may be the same or similar to the requirements for the knife or knives employed in the generalized cutting head.
It is desirable in planing to obtain the best surface finish possible. For example, lumber is graded according to surface finish, with higher grades being more valuable. However, prior art planing apparatus commonly results in fiber pulling around knots and swirled grain areas that lowers the quality of the surface finish. Sometimes, a knot is pulled entirely out of a piece of lumber as a result of planing, which drastically lowers the value of the piece.
Another problem with prior art planing apparatus is that the cutting heads induce movement of the wood as it is being cut, which also lowers the quality of the surface finish.
On the other hand, it is also desirable to minimize the cost of the planing apparatus, as well as the cost of its maintenance and repair. Accordingly, there is a need for a method and apparatus for planing an article of wood that provides for increased quality of surface finish at low cost.
The invention disclosed herein is a method and apparatus for planing an article of wood. Within the scope of the invention, there is a cutting head adapted for rotation about an axis, and at least one elongate knife including a linear cutting edge for cutting the wood. The cutting edge terminates at opposite ends of the knife in respective tips. The knife is held by the cutting head so that each tip is rotated about the axis of rotation at the same fixed radius. However, the cutting edge is misaligned by a predetermined bias angle with respect to the axis of rotation. Preferably, for a 1xc2xe-3xc2xdxe2x80x3 long knife, the angle of misalignment is between about 10 and 25 degrees.
Where a plurality of the cutting heads are stacked or ganged together, preferably, the angle of misalignment for the knives of some of the cutting heads is reversed from the angle of misalignment for the knives of others of the cutting heads.
Therefore, it is a principal object of the present invention to provide a novel and improved method and apparatus for planing an article of wood.
It is another object of the present invention to provide such a method and apparatus that provides for a high quality surface finish.
It is a still another object of the present invention to provide such a method and apparatus that provides such a surface finish at low cost.